JS数组方法shift()、unshift()用法实例分析

var arr1 = [1, 2, 3, 4, 'A', 'B', 'C']; 
var arr2 = [];
Array.prototype.copyShift = function() {
  var result = [],
    newArr = [];
  result = this[0];
  for(var i = 1; i < this.length; i++) {// 将数组的第二个至最后一项的值赋值给newArr
    newArr[newArr.length] = this[i];
  }
  for(var i = 0; i < newArr.length; i++) { //newArr赋值给原数组
    this[i] = newArr[i];
  }
  this.length = newArr.length;
  return result;
};
console.log(arr1.copyShift());  // 1
console.log(arr1); // [2, 3, 4, 'A', 'B']
console.log(arr2.copyShift()); // undefined
console.log(arr2); // []

var arr1 = [1, 2, 3, 4, 'A', 'B', 'C']; 
var arr2 = [];
Array.prototype.copyShift = function() {
  var result = [];
  result = this[0];
/* 
  for(var i = 1; i < this.length; i++) {// 将数组的第二个至最后一项的值赋值给newArr
    newArr[newArr.length] = this[i];
  }
  for(var i = 0; i < newArr.length; i++) { //newArr赋值给原数组
    this[i] = newArr[i];
  }
  this.length = newArr.length;
 */
  // 将数组的后一项赋值给前一项
  for(var i = 0; i < this.length; i++) {
    this[i] = this[i + 1];
  }
  if(this.length > 1) {//去掉数组最后一项
    this.length = this.length - 1;
  }
  return result;
};
console.log(arr1.copyShift());  // 1
console.log(arr1); // [2, 3, 4, 'A', 'B']
console.log(arr2.copyShift()); // undefined
console.log(arr2); // []

var arr1 = [1, 2, 3, 4, 'A', 'B', 'C']; 
var arr2 = [1, 2, 3, 4];
Array.prototype.copyUnshift = function() {
  var newArr = [],
    argLen = arguments.length,
    len = argLen + this.length;
  for(var i = 0; i < len; i++) {
/* 
    if(i < argLen) {
      newArr[i] = arguments[i];
    }
    else {
      newArr[i] = this[i - argLen];
    }
 */
    // 上述代码也可写为：
    newArr[i] = (i < argLen) "//img.jbzj.com/file_images/article/202001/2020118104647461.png" alt="" />



//同方法一一样，只不过是for循环以递减的形式
var arr1 = [1, 2, 3, 4, 'A', 'B', 'C']; 
var arr2 = [1, 2, 3, 4];
Array.prototype.copyUnshift = function() {
  var newArr = [],
    argLen = arguments.length,
    len = argLen + this.length;
  //同方法一一样，只不过是for循环以递减的形式
  for(var i = len - 1; i >= 0; i--) {
/*     if(i < argLen) {
      newArr[i] = arguments[i];
    }
    else {
      newArr[i] = this[i - argLen];
    } */
    // 上述代码也可写为：
    newArr[i] = (i < argLen) "htmlcode">

var arr1 = [1, 2, 3, 4, 'A', 'B', 'C']; 
var arr2 = [1, 2, 3, 4];
Array.prototype.copyUnshift = function() {
  var argLen = arguments.length,
    len = argLen + this.length;
  for(var i = len - 1; i >= 0; i--) {
/*     if(i > argLen - 1) {
      this[i] = this[i - argLen];
    }
    else {
      this[i] = arguments[i];
    }
 */
    this[i] = (i > argLen - 1) "//img.jbzj.com/file_images/article/202001/2020118104945635.png" alt="" />

感兴趣的朋友可以使用在线HTML/CSS/JavaScript代码运行工具：http://tools.jb51.net/code/HtmlJsRun测试上述代码运行效果。
更多关于JavaScript相关内容感兴趣的读者可查看本站专题：《JavaScript数组操作技巧总结》、《JavaScript遍历算法与技巧总结》、《javascript面向对象入门教程》、《JavaScript数学运算用法总结》、《JavaScript数据结构与算法技巧总结》及《JavaScript错误与调试技巧总结》
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                                    JS,数组方法,shift(),unshift() 
                                

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